A system using multiple carriers has been developed to support a higher data rate.
For example, 3rd generation partnership project (3GPP) long term evolution (LTE) is a system based on 3GPP technical specification (TS) release 8. The 3GPP LTE system supports only one bandwidth (i.e., one carrier) among {1.4, 3, 5, 10, 15, 20} MHz. In order to support a full bandwidth of 40 MHz, the multiple carrier system uses two carriers having a bandwidth of 20 MHz or uses 3 carriers respectively having bandwidths of 20 MHz, 15 MHz, and 5 MHz.
The multiple carrier system can support backward compatibility with respect to legacy systems, and can significantly increase a data rate by using multiple carriers.
Downlink power control is an operation in which a BS determines transmit power of a downlink channel and reports the determined transmit power to a UE. This is because a high-order modulation scheme (e.g., 16 quadrature amplitude modulation (QAM), 64 QAM, etc.) has a different transmit power level for each constellation point of a modulation symbol, and thus error-free decoding is possible only when the UE knows the transmit power level.
With the introduction of multiple carriers, a channel structure may vary. Accordingly, downlink power control also needs to consider the multiple carriers.